In systems now in use, digital data is transmitted from a transmitter to a receiver. The digital data received at the receiver is not easily recognized. This results in part from noise produced in the transmission of the data from the transmitter to the receiver. It also results in part from the fact that the digital data travels in different paths from the transmitter to the receiver. For example, the digital data preferably travels directly from the transmitter to the receiver. However, the digital data can also travel from the transmitter to positions misaligned with the transmitter and the receiver and then travel from the misaligned positions to the receiver.
This misalignment causes the data received at the receiver from the misaligned position to be out of phase with the signals passing directly from the transmitter to the receiver. This out-of-phase relationship makes it difficult to recover the data at the receiver. The problem is aggravated because the receiver can often receive the same data from a number of different misaligned positions in addition to the data passing directly from the transmitter to the receiver. The misalignment can cause the data transmitted from the transmitter to the receiver to fade because the phases of the misaligned signals are such that the amplitudes of the misaligned signals are subtracted from the amplitude of the signals translated directly from the transmitter to the receiver.
Attempts have been made to alleviate the problems of recovering data at the receiver when the data has been blurred by noise and by misalignments in phase. For example, in systems now in use for sending digital data from a controlled station (e.g., a transmitting station) to a controlling station (e.g., a receiving station), the digital data is provided with repetitive sequences of M modulations where M is a constant. Each of the M data modulations in each sequence is different from the other ones of the M modulations in the sequence. The M data modulations at the transmitter are provided in accordance with instructions from the controlling station (e.g. receiver). The modulated data is transmitted from the transmitter to the receiver in packets. In a first packet or sequence of packets, the data may be modulated with a first one of the M data modulations. In a second packet or sequence of packets, the data may be transmitted with a second one of the M data modulations. In a third one of the packets or sequence of packets, the data may be transmitted with a third one of the M data modulations.
In other systems now in use, the digital data in each packet or sequence of packets may be transmitted from the transmitter to the receiver at individual ones of N spreading codes. For example, the modulated data in a first one of the packets or sequence of packets may be transmitted from the transmitter to the receiver at a first one of the N different spreading codes. The data in a second one of the packets or sequence of packets may then be transmitted from the transmitter to the receiver at a second one of the N spreading codes rates. The data in a third one of the packets or sequence of packets may be subsequently transmitted from the transmitter to the receiver at a third one of the N spreading codes. Each spreading code may provide for a transmission of the data at a different rate. The N different spreading codes may be provided in accordance with instructions from the receiver.
The systems now in use and discussed in the previous paragraphs have reduced the problem of recovering data at a receiver, but have not solved the problem. It is still difficult to recover data at a receiver because of the proliferation in the reception at the receiver of out-of-phase data which clouds the reception and recovery of the in-phase data.
Several documents can be considered as prior art to the invention disclosed and claimed in this application. These are as follows:                (a) U.S. Pat. No. 5,541,955 issued on Jul. 30, 1996, to Jacobsmeyer for an Adaptive Data Rate Modem;        (b) An article-published on-pages 927–946 of the May, 1998, issue of IEEE Transaction on Information Theory. This article was written by Giusepper Caire et al and was entitled “Bit-Interleaved Coded Modulation”;        (c) An article published on pages 54–64 of the January, 2000, issue of IEEE Communications magazine. This article was written by Sanjiv Nanda et al and was entitled “Adaption Techniques in Wireless Packet Data Services”;        (d) An article published on pages 2223–2230 of the July, 1995, issue of IEEE Transactions on Communications. This article was written by W. Webb and R. Steel and was entitled “Variable Rate QAM for Mobile Radio”; and        (e) An article published on pages 1218–1230 in the October, 1997, issue of IEEE Transactions on Communications. This article was written by A. Goldsmith and S. Chaa and was entitled “Variable-Rate Variable-Power MQAM for Fading Channels”.        
The prior art references specified above in paragraphs (a) through (e) disclose systems for modulating data and also disclose systems for providing spreading codes. However, they do not disclose systems for providing a combination of data modulations and spreading codes. They further do not disclose systems which provide channel encodings with either data modulations or spreading codes or both data modulations and spreading codes. There is also no disclosure in the prior art specified above of particular techniques of combining data modulations and spreading codes to provide an optimal detection of the data even when the data is obscured by considerable amounts of multi-path fading.